The invention relates to a modulator intended for diverting a flow of pressurized fluid from the fluid supply circuit of a hydraulic motor. It also relates to a power-assisted steering circuit for a motor vehicle, the assistance of which is a function of the speed of the vehicle, this circuit employing such a modulator.
The U.S.-Patent Letters 4,561,521 makes known a power-assisted steering circuit of the above-mentioned type, which uses a modulator to divert, when the vehicle is at high speed, some of the pressurized assistance fluid towards the low-pressure fluid reservoir, so as to limit the assistance at high speed. This modulator is composed of a simple electrically controlled piston which may or may not close a port for discharging the fluid towards the low-pressure fluid reservoir.
Such a modulator requires a large actuating device because one of the faces of the piston receives the pressurized fluid permanently.
Furthermore, it is known that, in a power-assisted steering, it is desirable to keep the flow of fluid diverted at a given vehicle speed constant, despite the pressure variations which can come from the feed pump or from the circuit diverted downstream of the modulator, in order to preserve the assistance features. Now the modulator described in the above-mentioned document does not perform any function of regulating the flow.